[MARMAM] New publication on estimation of population size and trends for highly mobile species with dynamic spatial distributions

Charlotte Boyd - NOAA Affiliate charlotte.boyd at noaa.gov
Tue Nov 7 13:36:14 PST 2017


Dear MARMAM community

My coauthors and I are pleased to share our recent publication in *Diversity
and Distributions:*

Estimation of population size and trends for highly mobile species with
dynamic spatial distributions
.
Charlotte Boyd, Jay Barlow, Elizabeth A. Becker, Karin A. Forney, Tim
Gerrodette, Jeffrey E. Moore and André E. Punt.

Version of Record online: 17 OCT 2017 | DOI: 10.1111/ddi.12663

Aim: To develop a more ecologically realistic approach for estimating the
population
size of cetaceans and other highly mobile species with dynamic spatial
distributions.

Location: California Current Ecosystem, USA.

Methods: Conventional spatial density models assume a constant relationship
between
densities and habitat covariates over some time period, typically a survey
season.
The estimated population size must change whenever total habitat
availability
changes. For highly mobile long-lived species, however, density–habitat
relationships
likely adjust more rapidly than population size. We developed an integrated
population-redistribution model based on a more ecologically plausible
alternative hypothesis: (1)
population size is effectively constant over each survey season; (2) if
habitat availability
changes, then the population redistributes itself following an ideal free
distribution
process. Thus, the estimated relationship between densities and habitat
covariates
adjusts rather than population size. We constructed Bayesian hierarchical
models corresponding
to the conventional and alternative hypotheses and applied them to distance
sampling data for Dall’s porpoise (Phocoenoides dalli), a highly mobile
cetacean
with distribution patterns closely tied to cool sea-surface
temperatures.

Results: The Dall’s porpoise data provided strong support for the
hypothesis based on
an ideal free redistribution process. Our results indicate that the
population size of
Dall’s porpoise within the survey region was relatively stable over each
summer/fall
survey season, but the distribution expanded and contracted with the extent
of suitable
habitat. Over multiple survey seasons, the model partitioned variation in
observed
densities among three sources: variation in population size, the
density–habitat relationship
and measurement error, leading to lower and more ecologically plausible
estimates
of interannual variation in population size.

Main conclusions: We conclude that the integrated population-redistribution
model (IPRM) presented here represents an ecologically plausible model for
use in future assessments of the population size and dynamics of cetaceans
and other highly mobile
long-lived species with variable spatial distributions.

Keywords: Bayesian hierarchical model, California Current, Dall’s porpoise,
distance sampling, habitat model, spatial density model

The online version of the article can be accessed here:
http://onlinelibrary.wiley.com/doi/10.1111/ddi.12663/abstract

To request a pdf copy please email me at: charlotte.boyd at noaa.gov.

All the best

Charlotte

-- 
Charlotte Boyd PhD
Marine Mammal Laboratory
NOAA Alaska Fisheries Science Center
7600 Sand Point Way NE
Seattle WA 98115
Phone: 206-526 4046
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